using System;
using System.Web;

namespace Umbraco.Core.Cache
{
    /// <summary>
    /// Represents the application caches.
    /// </summary>
    public class AppCaches
    {
        /// <summary>
        /// Initializes a new instance of the <see cref="AppCaches"/> for use in a web application.
        /// </summary>
        public AppCaches()
            : this(HttpRuntime.Cache)
        { }

        /// <summary>
        /// Initializes a new instance of the <see cref="AppCaches"/> for use in a web application.
        /// </summary>
        public AppCaches(System.Web.Caching.Cache cache)
            : this(
                new WebCachingAppCache(cache),
                new HttpRequestAppCache(),
                new IsolatedCaches(t => new ObjectCacheAppCache()))
        { }

        /// <summary>
        /// Initializes a new instance of the <see cref="AppCaches"/> with cache providers.
        /// </summary>
        public AppCaches(
            IAppPolicyCache runtimeCache,
            IAppCache requestCache,
            IsolatedCaches isolatedCaches)
        {
            RuntimeCache = runtimeCache ?? throw new ArgumentNullException(nameof(runtimeCache));
            RequestCache = requestCache ?? throw new ArgumentNullException(nameof(requestCache));
            IsolatedCaches = isolatedCaches ?? throw new ArgumentNullException(nameof(isolatedCaches));
        }

        /// <summary>
        /// Gets the special disabled instance.
        /// </summary>
        /// <remarks>
        /// <para>When used by repositories, all cache policies apply, but the underlying caches do not cache anything.</para>
        /// <para>Used by tests.</para>
        /// </remarks>
        public static AppCaches Disabled { get; } = new AppCaches(NoAppCache.Instance, NoAppCache.Instance, new IsolatedCaches(_ => NoAppCache.Instance));

        /// <summary>
        /// Gets the special no-cache instance.
        /// </summary>
        /// <remarks>
        /// <para>When used by repositories, all cache policies are bypassed.</para>
        /// <para>Used by repositories that do no cache.</para>
        /// </remarks>
        public static AppCaches NoCache { get; } = new AppCaches(NoAppCache.Instance, NoAppCache.Instance, new IsolatedCaches(_ => NoAppCache.Instance));

        /// <summary>
        /// Gets the per-request cache.
        /// </summary>
        /// <remarks>
        /// <para>The per-request caches works on top of the current HttpContext items.</para>
        /// <para>Outside a web environment, the behavior of that cache is unspecified.</para>
        /// </remarks>
        public IAppCache RequestCache { get; }

        /// <summary>
        /// Gets the runtime cache.
        /// </summary>
        /// <remarks>
        /// <para>The runtime cache is the main application cache.</para>
        /// </remarks>
        public IAppPolicyCache RuntimeCache { get; }

        /// <summary>
        /// Gets the isolated caches.
        /// </summary>
        /// <remarks>
        /// <para>Isolated caches are used by e.g. repositories, to ensure that each cached entity
        /// type has its own cache, so that lookups are fast and the repository does not need to
        /// search through all keys on a global scale.</para>
        /// </remarks>
        public IsolatedCaches IsolatedCaches { get; }
    }
}